Step 1: Detect a Possible Outbreak

Illustration representing detecting a sickness by showing a stethoscope and a thermometer.

Detecting an outbreak is the first step in investigating a multistate foodborne outbreak. An outbreak with multiple sick people can be missed if they are spread out over a wide area. Outbreaks are detected by using public health surveillance methods, including PulseNet, formal reports of illnesses, and informal reports of illnesses.

How are outbreaks found?

One way health officials find outbreaks is through public health surveillance. By routinely gathering reports of illnesses, they know how many illnesses to expect in a given time period in a given area. If a larger number of people than expected appear to have the same illness in a given time period and area, it’s called a cluster. When an investigation shows that ill people in a cluster have something in common to explain why they all got the same illness, the group of illnesses is called an outbreak.

Key words:

Public health surveillance: Routine gathering of reports of illnesses by health professionals

Cluster: A larger number of people than expected with the same illness in a given time period and area

Outbreak: A group of illnesses in a cluster of people who have something in common that caused the illness

PulseNet: A national laboratory network that connects local and multistate foodborne illness cases to detect outbreaks

Informal reports of outbreaks

Informal reports occur when members of a community call the local health department to report suspected food-related illnesses. For example, this might happen if several people got sick after eating at a group dinner.

Formal reports of outbreaks

Doctors and microbiologists in each state must formally report infections that are on a list of notifiable diseases when they diagnose them in patients. This list includes many foodborne illnesses. As public health officials look at disease reports, they may notice that the number of people with a particular illness is higher than expected. Formal reports also occur when a health professional realizes that he or she is seeing more cases of an illness than would be expected and calls the health department directly.

What happens when a doctor suspects a person has a foodborne illness?

  • The patient may be asked to submit a stool sample (or some other type of sample) to help figure out what germ is making them ill.
  • The patient’s sample is sent to a clinical laboratory.
  • The clinical laboratory tests and may identify the germ (for example a bacteria or virus) that is making them ill.
  • The clinical laboratory tells the doctor’s office the results of their testing so the doctor can treat the illness.
  • The germ may then be sent to the state public health laboratory for DNA fingerprinting.

For some pathogens, like the bacteria Salmonella and E. coli O157, public health laboratories State laboratories report their DNA fingerprinting results to the PulseNet database.

What is the PulseNet database?

  • PulseNet is a national laboratory network that connects foodborne illness cases to detect outbreaks. PulseNet uses DNA fingerprinting, or patterns of bacteria making people sick, to detect thousands of local and multistate outbreaks. It can take several weeks from the ay the person became ill to the day the results of fingerprinting the bacteria are added to the PulseNet database.
  • Since the network began in 1996, PulseNet has improved our food safety systems through identifying outbreaks early. This allows investigators to find the source, alert the public sooner, and identify gaps in our food safety systems that would not otherwise be recognized.